Adjustable voltage autotransformer having a winding provided with a commutating track



Aprll 1964 A. E. SNOWDON ETAL 3,128,442

ADJUSTABLE VOLTAGE AUTOTRANSFORMER HAVING A WINDING PROVIDED WITH A COMMUTATING TRACK Filed May 2, 1961 INVENTORS ,Amf/zw" fl Snow/dam P/zilmor'e l2". Ja/ypfion/ Mme J4 Gdanzanelt BY M ATTORNEYS United States Patent ADJUSTABLE VOLTAGE AUTOTRANSFORMER HAVING A WINDING PRGVIDED WITH A CUM- MUTATING TRACK Arthur E. Snowdon, Philmore E. Johnson, and Nimo A. Gianzinetti, all of Bristol, C0nn., assignors to The Superior Electric Company, Bristol, Conn, a corporation of Connecticut Filed May 2, 1961, Ser. No. 107,204 4 Claims. (Cl. 336-1,49)

The present invention relates to an adjustable voltage autotransformer of the type having a winding wound on a magnetic core, a commutating track formed on the winding and a brush riding in electrical engagement on the track. Movement of the brush on the winding effects a change in the voltage.

While the presently employed construction of an adjustable voltage autotransformer of the above type has been found to be satisfactory, problems have arisen with respect to the construction. One problem arises in connection with the requiring of many different models of autotransformers wherein the only difference between the models is in the length of the shaft between the autotransformer and a knob used to control it. This difference is required to enable the autotransformer to be suitable for various panel thicknesses where, for example, the autotransformer is mounted on the back of a panel and the knob is mounted on the other or front side of the panel. Moreover, while the heretofore known autotransformers have been durable in use, it has been found that in some instances the locking joint between the brush holding means and the shaft, and the knob and the shaft has become sufficiently mutilated to prevent operation of the autotransformer, such mutilation occurring in the insulation that is included in the locking joints to insulate the other parts from the voltage of the shaft.

It is accordingly an object of the present invention to provide in an adjustable voltage autotransformer for a construction of the autotransformer which obviates the above-noted deficiencies.

Another object of the present invention is to provide in an autotransformer, as above noted, for a metal shaft for rotating the brush in which the shaft is insulated from the voltages in the autotransformer.

A further object of the present invention is to provide an improved construction of an adjustable voltage autotransformer which is relatively economical to manufacture and durable in use.

In carrying out the present invention, a feature thereof resides in the manner in which the coil and the shaft are interconnected such that a shaft of a desired length may be used with the coil and be insulated from the voltages in the autotransformer. This is accomplished according to the present invention of the construction of an adjustable voltage autotransformer by providing a coil formed of an annular core on which a toroidal Winding is held by a plastic bushing which abuts one end of the coil and extends through the central hole and has another base member secured thereto to accordingly clamp the coil between these members. The bushing is formed with a central aperture and within this aperture there is positioned a metal tube with the tube being formed at one end to have a brush carrying radiator connected therethrough through a plastic disk. A shaft is positioned within the metal tube and is secured thereto as by a setscrew passing through the plastic disk and the metal tube. Thus an autotransformer may have a shaft of varying length simply by the insertion of a rod of the desired length into the above-noted construction and have the rod locked in place by the shaft locking screws.

It will be moreover clear that though the shaft engages 3,128,442 Patented Apr. 7, 1964 the metal sleeve, that the metal sleeve is insulated from the current carrying members and hence there is eliminated the need for insulating inserts on the shaft which may become mutilated and in addition eliminates hazardous conditions.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is an axial section of an adjustable voltage autotransformer made according to the present invention.

FIG. 2 is an end view taken on the line 2-2 of FIG. 1.

FIG. 3 is a section taken on the line 33 of FIG. 1.

Referring to the drawing, the autotransformer is generally indicated by the reference numeral 10 and includes an annular core 11 formed of spirally wound magnetic material. Annular end forms 12 are positioned against the ends of the core and a winding 13 is toroidally wound about the core and end forms. The core and winding are herein referred to as the coil of the autotransformer.

The Winding 13 is formed to provide a commutating track generally indicated by the reference numeral 14 on which a carboniferous brush 15 is moved by actuation of a knob 16 or other rotative means such as a motor. Connections to the autotransformer are made through terminals 17 mounted on a terminal board 18. The above construction is well known in the art and no further amplification is believed needed.

In accordance with the present invention the brush and the knob are interconnected in such a manner that while metal parts are employed in the interconnection, the knob and knob connections are insulated from the current carrying brush. This is accomplished according to the present invention by providing a bushing 19 formed of electrical insulating plastic material having a flanged portion 20 which abuts one end of the coil and is provided with a threaded end portion 21 that extends through an aperture 22 formed in a relatively'square metallic end or base plate 23. A nut 24 screws on the threaded portion 21 to axially clamp the base plate 23 and the flanged portion 20 together against the ends of the coil.

Additionally there is provided an insulating washer 25 between the coil and the metal base plate 23 with a locking projection 26 formed in the base plate 23 extending through an aperture 27 in the washer 25 into a hole 28 formed in the end form 12 to thereby prevent relative rotation of the parts. The terminal board 18 is secured to one edge of the base plate 23.

The plastic bushing 19 is formed with an axial aperture 29 that is coaxial with the axis of the coil. Positioned within and mounted for relative rotation in the aperture 29 is a sleeve which in the particular embodiment of the invention herein described consists of a metal tube 30 having at one end a disk 31 formed of electrically insulating plastic material secured thereto as by setscrews 32 that thread through apertures 32a formed in the tube 30 for reasons that will hereinafter be apparent. The plastic disk, as by rivets 33, has secured thereto a flat, circular radiator 34 on which is mounted the carboniferous brush 15 such that rotation of the radiator causes the brush 15 to rotate on and be in electrical conduction with the com mutator track 14. The rivets 33 further secure a conducting disk 35 of metal to the radiator while secured on the flanged portion 20 of the bushing 19 is a terminal 36 having an annular part 37 that encircles the hub of the disk 31 and tube 30. A bowed, annular metal spring 38 positioned between the conducting disk 35 and the annular portion 37 of the terminal 36 conducts electricity from the conducting disk 35 to the annular portion 37 of the terminal 36 and is assured constant contact by use of bowed C-ring 30a positioned at the righthand end of the tube 30 which urges the tube 30 rightward against the end of the bushing 19. A screw 36b secures the terminal 36 to the end form and it will be clear from FIG. 3 that the 'board 18.

The above construction provides for rotation of the tube 30 to move the brush 15 with the tube 30 being electrically insulated from the current carrying parts of the brush 15. In order to achieve the above-recited object of the present invention, a cylindrical rod or shaft 39 is positioned within the tube 30 and secured'thereto by the setscrews 32. The other end of the shaft 39 may have secured thereto the knob 16 as by a 'setscrew 40. It will thus be appreciated that the present invention obviates the need for having many special autotransformers with different shaft lengths since the same autotransformer if made according to the present invention maintains the same parts except for the length of the shaft 39 which may be easily changed simply by the insertion of a rod of the desired size in the tube 30 looking the setscrew 32 thereagainst, It will moreover be clear that the setscrews 32 and 40 both bear against the metal shaft 39 rather than insulating plastic inserts formed in the shaft 39 since according to the present invention the shaft 39 is electrically insulated from the brush current.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others. r

We claim:

1. An adjustable voltage autotransformer comprising a coil having an annular core of magnetic material and a Winding wound on said core with a commutating track formed on the winding, an end plate abutting one end of the coil, a member formed of insulating material having an end abutting the other end of the coil and having a portion extending axially through the center of the coil and being formed with an axial aperture, means interconnecting the end plate and the member to clamp the coil therebetween, a tube rotatably mounted in said axial aperture, a brush engageable with the commutatin'g track, means mounting the brush on said tube for movement therewith and including means insulating the tube from ,4 the current through the brush, and a shaft positioned in said tube and secured thereto for movement therewith.

2. An adjustable voltage autotransformer comprising a coil having an annular core of magnetic material and a winding wound on said core with a cornmutating track formed on the winding, an end plate abutting one end of the coil, a member formed of insulating material having an end abutting the other end of the coil and having a portion extending through the center of the coil, means interconnecting the end plate and the member to clamp the coil therebetween, a sleeve mounted in said member for relative rotation therebetween, a brush engageable with the c'ommutating track, means including" an insulating disk mounting the brush on said sleeve for movement therewith with the sleeve being electrically insulated from the brush, and a shaft positioned in said sleeve and secured thereto for movement therewith.

3. The invention as defined in claim 2 in which the means that secures the shaft to' the sleeve also secures the disk to the sleeve.

4. An adjustable voltage autotransformer comprising a coil having an annular core of magnetic material and a Winding wound on said core with a commutating track formed on the winding, an end plate abutting one end of the coil, a member formed of insulating material having. an end abutting the other end of the coil and having a portion extending through the center of the coil, means interconnecting the end plate and the member to clamp the coil therebetween, a sleeve mounted in said member for relative rotation therebetween, a brush engageable with the lcom'mutating track, means mounting the brush on' said sleeve for movement therewith and including a conducting disk electrically connected to the brush, but

electrically insulated from the sleeve a conducting terminal secured on the member, means electrically connecting the conducting disk to the conducting terminal for transferring current from the brush to the terminal, and a shaft positioned in said sleeve and secured thereto for movement therewith.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ADJUSTABLE VOLTAGE AUTOTRANSFORMER COMPRISING A COIL HAVING AN ANNULAR CORE OF MAGNETIC MATERIAL AND A WINDING WOUND ON SAID CORE WITH A COMMUTATING TRACK FORMED ON THE WINDING, AN END PLATE ABUTTING ONE END OF THE COIL, A MEMBER FORMED OF INSULATING MATERIAL HAVING AN END ABUTTING THE OTHER END OF THE COIL AND HAVING A PORTION EXTENDING AXIALLY THROUGH THE CENTER OF THE COIL AND BEING FORMED WITH AN AXIAL APERTURE, MEANS INTERCONNECTING THE END PLATE AND THE MEMBER TO CLAMP THE COIL THEREBETWEEN, A TUBE ROTATABLY MOUNTED IN SAID AXIAL APERTURE, A BRUSH ENGAGEABLE WITH THE COMMUTATING TRACK, MEANS MOUNTING THE BRUSH ON SAID TUBE FOR MOVEMENT THEREWITH AND INCLUDING MEANS INSULATING THE TUBE FROM THE CURRENT THROUGH THE BRUSH, AND A SHAFT POSITIONED IN SAID TUBE AND SECURED THERETO FOR MOVEMENT THEREWITH. 